1. Field of the Invention
The present invention relates to syringe fluid dispensers for dispensing controlled fluid doses and, more particularly, to apparatus for driving the syringe plunger of such dispensers.
2. Description of the Prior Art
Numerous fluid dispensing systems have been developed for medical, clinical, and laboratory applications requiring the dosing, mixing, or diluting of predetermined and minute quantities of various fluids. Typically, such dispensers include a syringe having a movable plunger which is driven longitudinally in opposite intake or discharge directions by a small bidirectional motor mechanically coupled to the plunger.
In one commercially available dispenser of the foregoing type, the mechanical coupling between motor and plunger is provided by a movable shaft. The shaft is movable in the same longitudinal direction as the plunger and is coupled thereto by a drive arm extending laterally between the shaft and the plunger. The drive arm carries a rack gear for driving the shaft and hence the plunger in the longitudinal direction in response to a turning of a mating pinion gear.
In the commercially available dispenser, the shaft slides within two fixed bearings secured to the frame of the dispenser. To accommodate maximum travel of the plunger in the syringe, the bearings are spaced apart by at least the maximum length of such plunger travel between limit positions. Thus arranged, the length of the shaft is approximately twice that of the maximum plunger travel. As a consequence, to accommodate the length of the shaft and the travel thereof in driving the plunger between limit positions, it is required that the housing for the dispenser have an internal height or width at least three times the maximum plunger travel. This results in a relatively larger and bulky housing for the dispenser, particularly when compared with the actual travel of the syringe plunger controlled thereby.